Starter

In pairs try and explain….

What current is,

What electric charge is,

Why electrons are negatively charged,

Why are electrons called electrons.

1.1.4 Projectile Motion CHARGE!

At GCSE you had to KNOW about electricity.

At AS Level you have to UNDERSTAND electricity.

G482

Unit G482: Electrons, Waves and Photons

• Module 1: Electric current• 2.1.1 Electric current

• Module 2: Resistance• 2.2.1 Circuit symbols• 2.2.2 E.m.f. and p.d.• 2.2.3 Resistance• 2.2.4 Resistivity• 2.2.5 Power

• Module 3: DC circuits• 2.3.1 Series and parallel circuits• 2.3.2 Practical circuits

Learning outcomes

You should all be able to:• explain that electric current is a net flow of

charged particles;• explain that electric current in a metal is

due to the movement of electrons, whereas in an electrolyte the current is due to the movement of ions;

• explain what is meant by conventional current and electron flow;

Extended Learning task

• Read the specification for G482 Electrons, Waves and Photons.

• In Advanced Physics for You read pages 190 – 195.

• Take appropriate notes that you feel will help you understand current and charge.

• Complete questions 1 – 6 on page 204.

Explain how a charged rod can attract a neutral piece of paper.

How large a piece of paper can you pick up?

Explain how a charged rod can attract a neutral piece of paper.

How large a piece of paper can you pick up?

Learning outcomesYou should be able to:• select and use the equation ΔQ = IΔt; • define the coulomb; • recall and use the elementary charge

e = 1.6 × 10-19 C. • describe how an ammeter may be used to

measure the current in a circuit; • describe Kirchhoff’s first law and appreciate

that this is a consequence of conservation of charge;

Key DefinitionKey Definition

1 coulomb is the amount of charge that passes a point when a current of 1 ampere flows for 1 second.

The challenge

• Gustav Kirchhoff said that: “The sum of currents flowing into a point equals the sum of the currents flowing out of that point.”

• You are to set up a number of circuits to prove Kirchhoff’s 1st law

• Think about the resources you have available for your group and the data you need to collect.

Spooning amounts of charge

link to earth socket

5 kV supply

internal 50M resistor

bare 4mm plug

044

coulomb meter

insulating handle

metal disk on 4mm plug

A spoonful of electrons makes the medicine go down

Knowing that the charge on an electron is –1.6 x 10–19 C, you can calculate the number of electrons in a 'spoonful' of charge. A typical spoonful of negative charge is –2 nC. So the number of electrons is…..

1. Convert 25 mA to A

2. Convert 0.50 A to mA

3. A torch bulb passes a current of 120 mA.

(a) How many coulombs of charge flow through the lamp in 1 minute?

(b) How many coulombs of charge flow through the lamp in 1 hour?

(c) How many electrons leave the negative terminal of the cell each second?

4. A car battery is rated as 36 A h. In principle this means it could pass a current of 1 A for 36 h before it runs down. How much charge passes through the battery if it is completely run down?

5. An electron beam in a beam tube carries a current of 125 A.

(a) What charge is delivered to the screen of the tube every second?

(b) How many electrons hit the screen each second?

Solutions to introductory questions on charge and current

1. 0.025 A

2. 500 mA

3. (a) Q = It = 0.120 60 = 7.2 C

(b) Q = It = 0.120 60 60 = 432 C

(c) N = Q/e = It/e = (0.120 1) / 1.6 10-19 = 7.5 1017 s-

1

4. Q = It = 36 60 60 = 129 600 = 130 000 (2 sf.)

5. (a) Q = It = 1.25 10-4 1 = 1.25 10-4 C

(b) N = Q/e = 1.25 10-4 / 1.6 10-19 = 7.8 1014 s-1

Learning outcomes

State what is meant by the term mean drift velocity of charge carriers 

Select and use the equation I = Anev 

Describe the difference between conductors, semiconductors and insulators in terms of the number density n.